1. Field of the Invention
This invention concerns a planar-mounted optical waveguide transmitter-receiver module, in which silicon or other substrates, separated into a plurality of substrates, and an optical waveguide (planar lightwave circuit) substrate (hereafter “PLC substrate”), are hybrid-integrated.
2. Description of Related Art
Optical terminal devices for use in optical subscriber systems are subjected to such demands as smaller integration sizes, multi-functionality, and reduced prices. Optical modules with optical waveguides as devices effective for satisfying such demands are coming into widespread use. Conventional silicon platform structures, in which optical waveguides and silicon substrates are united, have problems which include complexity of manufacturing processes and limitations on the manufactured quantity per unit wafer. For this reason, various planar-mounted optical waveguide transmitter-receiver modules in which a silicon substrate and a PLC substrate are hybrid-integrated have been proposed. Below, the structure of conventional optical waveguide transmitter-receiver modules is explained, referring to FIGS. 1 through 3.
FIG. 1 is a perspective view of an optical waveguide transmitter-receiver module, representing conventional synchronous-transfer mode passive optical networks (hereafter “STM-PON”) and π-PON systems.
This optical waveguide transmitter-receiver module has a silicon substrate 1, and an optical waveguide layer 2 is formed on this silicon substrate 1. The optical waveguide layer 2 is formed by, for example, deposition of quartz glass by sputtering methods and execution of vitrification processing of this deposited layer by means of high-temperature annealing. In this way, the optical waveguide layer 2 and silicon substrate 1 are formed as a unit to constitute the silicon platform substrate. A dual-branching optical waveguide 3 is formed within the optical waveguide layer 2 for use in bidirectional communication. The optical waveguide 3 has entry and exit end faces 3a to 3d. A groove is cut in the branch part 3e, and a wavelength-selection filter embedded therein. The device with this filter 4 removed is a π-PON device.
On the silicon substrate 1, a semiconductor laser or other light emitting element 5 and photodiode or other photo-receiving element 6 are fixed in place, by soldering or other means, to oppose the end faces 3a, 3b of the optical waveguide. The module is designed to enable the connection of optical fibers to the end faces 3c, 3d of the optical waveguide 3 by means of optical connectors.
For example, in an optical waveguide transmitter-receiver module for use in STM-PON systems, a light emitting element 5 and photo-receiving element 6 operate at different times (with different timing). When the light emitting element 5 operates, light is emitted from this light emitting element 5, and this light is incident on the end face 3a of the optical waveguide 3. Light incident on the end face 3a is transmitted within the optical waveguide 3, is wavelength-selected by the filter 4 provided at the branch part 3e, and is, for example, emitted from the end face 3c and sent to an optical fiber via an optical connector. On the other hand, light sent from an optical fiber is incident on, for example, the end face 3c via an optical connector. The incident light is wavelength-selected by the filter 4, and emitted from the end face 3b. The emitted light is received by the photo-receiving element 6, converted into an electrical signal, and output. Light of different wavelengths sent from an optical fiber, after incidence on the end face 3c, is wavelength-selected by the filter 4 and emitted from the end face 3d. 
FIG. 2 is a perspective view of an optical waveguide transmitter-receiver module compatible with a conventional asynchronous-transfer mode passive optical network (asynchronous transfer mode PON, hereafter “ATM-PON” systems).
This optical waveguide transmitter-receiver module for ATM-PON systems has nearly the same optical component configuration as in FIG. 1, but the shape of the optical waveguide 3A formed within the optical waveguide layer 2, and the fixed positions of the emissive element 5 and photo-receiving element 6, are different from those of FIG. 1. That is, on a silicon platform substrate in which the optical waveguide 3A and silicon substrate 1 are formed integrally, entry/exit end faces 3b to 3d are formed in the optical waveguide 3A. The photo-receiving element 6 is fixed in place opposing the end face 3b on the silicon substrate 1, by soldering or other means, and the light emitting element 5 is fixed in place on the silicon substrate 1 opposing the end face 3d, distant from the other end face, by soldering or other means. The module is designed such that an optical fiber can be connected, by means of an optical connector, to the end face 3c. 
In this optical waveguide transmitter-receiver module for ATM-PON systems, the light emitting element 5 and photo-receiving element 6 operate simultaneously. Consequently, resistance to crosstalk between optical transmission and reception signals is required. For this reason, the light emitting element 5 and photo-receiving element 6 are mounted on the silicon substrate as far apart as possible, and by this means, the adverse effects of electrical crosstalk induced by electromagnetic coupling via the silicon substrate between the light emitting element 5 and photo-receiving element 6 are reduced.
FIG. 3 is a perspective view of a conventional optical waveguide transmitter-receiver module for π-PON systems, with hybrid-integration of silicon substrate and PLC substrate.
This optical waveguide transmitter-receiver module for π-PON systems has a silicon substrate 7 with flat surface. On the flat surface of this silicon substrate 7 is formed by etching a V-shaped etched groove (hereafter “V groove”) 8, for aligned mounting of an optical fiber. A light emitting element 5 and photo-receiving element 6 are fixed in place on the silicon substrate by soldering or other means. A PLC substrate 9, manufactured in advance, is fixed in place by resin, soldering or other means on the silicon substrate 7, opposing the light emitting element 5, photo-receiving element 6, and V groove 8. The PLC substrate 9 is formed by layered deposition of an optical circuit, to serve as the optical waveguide 3B, on parent-material or matrix substrate, primarily silicon, quartz, or a polyimide. The optical waveguide 3B is provided with entry/exit end faces 3a to 3c opposing the light emitting element 5, photo-receiving element 6, and V groove 8.
In this optical waveguide transmitter-receiver module for π-PON systems, an optical fiber is inserted into the V groove 8, and is bonded using a resin. For example, light emitted from the light emitting element 5 is incident on the end face 3a of the optical waveguide 3B. The incident light passes through the branch part 3e, is emitted from the end face 3c, and is sent to the optical fiber in the V groove 8. On the other hand, light sent from the optical fiber is incident on the end face 3c of the optical waveguide 3B. The incident light passes through the branch part 3e, and is emitted from the end face 3b. The emitted light is received by the photo-receiving element 6, and is converted into an electrical signal and output.
However, the conventional optical waveguide transmitter-receiver modules of FIGS. 1 to 3 have the following problems (1) to (3).
(1) Case of the optical waveguide transmitter-receiver module structure of FIG. 1 and FIG. 2
An optical waveguide transmitter-receiver module such as that of FIG. 1 and FIG. 2 adopts a silicon platform structure, in which the optical waveguide 3, 3A and silicon substrate 1 are integrated. That is, numerous optical waveguide transmitter-receiver module areas are provided on a silicon wafer, for example, and wiring patterns and other electrical circuit parts are formed in each of these areas on the silicon substrate 1. At the same time, quartz glass or other material is deposited by sputtering methods to form the optical waveguide layer 2, and thereafter a light emitting element 5 and photo-receiving element 6 are fixed in place on the silicon substrate 1 by soldering or other means. Consequently the manufacturing process is complex, and moreover each optical waveguide transmitter-receiver module area formed on the wafer must be made slightly larger in order to expedite manufacturing processes. Hence such problems as limits on the quantity manufactured per unit wafer arise.
Moreover, in manufacturing processes for optical waveguide layers 2, high-temperature annealing processing must be used to execute vitrification of quartz waveguide crystals. However, if such high-temperature annealing is performed, defects occur in the silicon crystal of the silicon substrate 1, so that highly precise formation of the V groove by etching is made difficult, and consequently the realization of a receptacle structure (an optical connector structure having a function for optical fiber attachment and removal) becomes difficult. Further, when connecting an optical fiber array to the end faces 3c, 3d of the optical waveguide 3, 3A, optical core-aligned connection in order to match the optical axes is essential; and for this reason, connection tasks have required much care.
(2) Case of optical waveguide transmitter-receiver modules for ATM-PON systems of FIG. 2
Since a light emitting element 5 and photo-receiving element 6 are operated simultaneously, superior cross-talk performance is required for the transmitting and receiving signals. Therefore, the decrease of electric cross-talk between the light emitting element 5 and the photo-receiving element 6 mounted on the silicon substrate 1 must be attained by making the dimensions of the silicon substrate larger for increasing the distance between the positions where the elements 5 and 6 are mounted, and, for this reason, the module becomes large.
(3) Case of optical waveguide transmitter-receiver modules for π-PON systems of FIG. 3
In these optical waveguide transmitter-receiver modules for π-PON systems, the silicon substrate 7 and PLC substrate 9 are manufactured separately and independently, so that manufacturing processes can be simplified, and manufacturing quantities per unit wafer can be increased. Further, the V groove 8 is formed in integral fashion on the silicon substrate 7, so that by inserting an optical fiber into this V groove 8 and bonding with resin, the optical axes of this optical fiber and the end face 3c of the optical waveguide 3B are aligned; consequently optically non-aligned mounting of the optical fiber is possible. However, even in the case of this optical waveguide transmitter-receiver module for π-PON systems, as with (2) above, when using this model in an ATM-PON system, the dimensions of the silicon substrate 7 must be made large in order to secure resistance to electrical crosstalk over the silicon substrate 7 between the light emitting element 5 and photo-receiving element 6. Further, it is structurally difficult to insert the wavelength-selection filter 4 into the PLC substrate 9, and so there is the added problem that versatility of support for STM and ATM is lacking.